Leptospira, Treponema, and Borrelia are the major genera of the pathogenic spirochetes. We do not understand some of the most fundamental aspects of their biology of their mechanisms of pathogenesis. One unique aspect of all spirochetes is their rapid motility. We are using a genetic-biochemical approch to determine how they swim. Our model system is Leptospira interrogans, as it is readily manipulated in the laborary. We have obtained genetic evidence for a relationship between the axial filaments (AFs) and the motility of spirochetes. Motility mutants of L. interrogans were isolated. The AFs from these mutants were found to morphologically differ from those of the wild-type. Revertant analysis indicated that the mutants had pleiotropic mutations which involved motility, hook- and spiral- shaped ends, and AF structure. Based on these results, and in collaboration with another laboratory, we proposed a model of L. interrogans motility. Our major objective now is to test this model. The approaches we are using are isolating and characterizing new motility and chemotactic mutants, attaching latex beads to swimming cells and recording their movement by videotape and by cinematography, and characterizing the AF proteins of the mutants, revertants, and the wild-type by electrophoresis and tryptic fingerprint analysis. Our latex bead study revealed a capping-like phenomenon in L. interrogans. When antibody-coated latex beads were attached to swimming cells, the beads were displaced from the front-end of the cell to the back-end. If a cell is attached to an antibody-coated latex bead which is adhering to a glass surface, the cell swims back and forth across the surface of the bead. We propose that the antigen reacting with the antibody on the bead is moving laterally through the outer membrane sheath as the cell swims. We have recorded the movement of the cells with attached beads by videotape, and we are now testing this proposal.